1. Field of the Invention
The immune system is an incredibly sophisticated organization of cells, secreted factors and responses for protecting vertebrates against disease caused by pathogens or toxins. The fact that mammals are subject to disease, but survive in most instances, demonstrates both the fallibility of the system and its extraordinary capabilities. The immune system has found wide application for both in vivo and in vitro purposes, where vaccination, passive immunization, and production of antibodies for in vitro diagnostics, histology, cytology, and the like find application. With the advent of monoclonal antibodies, the immune system has seen an extraordinary expansion of its utilization for the production of monoclonal antibodies for a wide variety of purposes, where polyclonal antibodies were inadequate.
The immune system is complex and is not fully understood. The manner in which the immune system recognizes foreign immunogens from host peptides and saccharides has still not been elucidated, but is the subject of extensive investigation. Numerous instances exist where a mammalian host is subjected to foreign proteins, where only a weak or undetectable immune response is obtained. Many vaccines are based on the use of attenuated organisms, which carry with them the possibility of a virulent organism, which can result in infection upon immunization. In many instances, it is desirable to immunize with a surface protein or immunogenic portion thereof, but this is frequently found to be unsatisfactory due to a weak response or failure to produce antibodies to the relevant epitopic site. Many proteins or epitopic sites are found to be weakly immunogenic, so that when injected into a xenogeneic host, little if any neutralizing antibodies are obtained to the site(s) of interest.
It is therefore of great interest to be able to prepare compositions which demonstrate high immunogenicity to an epitopic site of interest. In this manner, one can obtain an enhanced immune response upon vaccination, provide antibodies which will be active in passive immunization and produce antibodies to what are otherwise weakly immunogenic epitopic sites in conventional hosts employed for the production of antibodies. Further, it would be preferable to produce compositions containing epitopic sites from more than one infectious agent. These compositions could then be utilized as polyvalent vaccines, allowing for less expensive, more efficient, and safer immunization regimens.
2. Description of the Relevant Literature
The entire genome of Hepatitis B virus has been cloned in E. coli and its nucleotide sequence has been determined (Valenzuela et al., Nature (1979) 280:815-819; Valenzuela et al., Animal Virus Genetics (1980) pp. 57-70). Hepatitis B surface antigen particles have been synthesized and assembled in the yeast S. cerevisiae (Valenzuela et al., Nature (1982) 298:347-350). The synthesis and assembly in yeast of Hepatitis B surface antigen particles containing the pre-surface antigen region has been described in copending application Ser. No. 621,756, filed on Jun. 18, 1984, entitled "Hepatitis Surface Antigen Particle Vaccine." The cloning of the Herpes Simplex virus glycoprotein D gene in E. coli and the gene nucleotide sequence has been reported (Watson et al., Science (1982) 218:381-384). The cloned glycoprotein D gene has been expressed in yeast as reported in copending application Ser. No. 631,669, filed Jul. 17, 1984, entitled, "Improved Expression of Glycoprotein D of Herpes Simplex Virus."
The sequence of the circumsporozoite (CS) protein for the human malarial parasite Plasmodium falciparum has been cloned (Dame et el., Science (1984) 225:593 and Enea et al. ibid p. 628). CS proteins from P. falciparum and P. Knowlesi have been expressed in Escherichia coli (Young et al., Science (1985) 228:958) and yeast (Sharma and Godson, Science (1985) 228:879). Also, synthetic peptiedes from the CS protein of P. falciparum were found to be immunogenic for mice and rats (Ballou et al., Science (1985) 228:996). All of the above relevant disclosures are incorported herein by reference.